New york cheesecake

Melt the butter in a medium pan. Remove the pan from the heat and stir in the biscuit crumbs, sugar, cocoa powder and chocolate chips.

Pre-heat the oven to 240C/gas 9. Line the base of a 23cm spring form cake tin with non-stick parchment and brush the sides of the tin with melted butter.

Press the biscuit crumb mixture onto the cake tin base - don't press it down too firmly though. Leave to one side while you make the filling.

Using an electric whisk, beat the cream cheese until soft. Gradually add the sugar, followed by the flour, vanilla, and lemon zest and juice. Add the eggs and extra yolk, a little at a time.

Stir in the soured cream and pour the cheesecake mixture into the prepared cake tin - over the biscuit crumbs. Tap the tin on the counter - this removes any air bubbles and ensures an even rise. Set the tin on a baking tray.

Bake in a hot oven for 10 minutes, then reduce the temperature to 90C/gas 1/4 and continue cooking for 25 minutes. By this time, the cheesecake should be golden and lightly set. Turn off the oven and leave the cheesecake to cool down slowly for 40 minutes. This prevents any cracking occurring on the surface. Remove from the oven and leave to cool completely.

For the topping, mix the soured cream with the sugar and lemon juice, and spread over the cake.

Chill the cheesecake, preferably overnight. To serve, run a round-bladed knife around the cake tin edges and unlock the sides of the cake tin. Slide the cheesecake onto a serving plate and cut into generous-sized portions. This dessert goes really well with heaps of fresh blueberries.